The invention relates to hydraulic lift mechanism wherein lift is accomplished through a continuous cyclic succession of vertical reciprocation. And the invention will be particularly described in application to the kind of vertical reciprocation involved in the pumped recovery of oil from one or more well casings.
The conventional oil-well pumping mechanism involves substantial frame structure at the well head, mounting a large beam, counterweighted at one end, and from the other end of which a pumping piston with associated check valve is suspended via a polish rod to a pumping depth which may be as much as or more than a mile beneath the well head. The beam is driven in angular oscillation by one of a variety of continuously running prime movers, such as a diesel engine or an electric motor having crank and link connection to the counterweighted half of the beam. There have been situations in which the polish rod has been connected to the piston rod of a hydraulic cylinder, and in that event the continuously running prime mover drives a pump, connected to the cylinder by suitably controlled valving to develop the vertically reciprocating strokes needed for pumping.
The disadvantage of the purely mechanical structures is that they are bulky, cumbersome, and relatively expensive in regard to both initial investment and maintenance. The disadvantage of the indicated hydraulically operated system is that prime-mover power must be of sufficiently great capacity to provide lift for the polish rod and its piston, plus the pumped column of oil, throughout the lifting stroke of the pumping cycle. And if hydraulic actuation has been provided as the means of operating a reciprocating beam, then the above-expressed disadvantages of a mechanically driven beam apply.